In April 1898, the Navy chartered four large passenger liners for conversion to auxiliary cruisers. USS Harvard and Yale were distinctive ships, with three smokestacks and "clipper" bows. Saint Louis and Saint Paul had a more "modern" appearance, with two stacks and plumb bows.

All four were very active in the Caribbean, searching for the Spanish fleet, patrolling, blockading and cutting telegraph cables. On 22 June, Saint Paul fought a sharp engagement with Spanish warships off San Juan, Puerto Rico. Harvard and Saint Louis were present at the battle off Santiago, Cuba, on 3 July. With the elimination of Spanish naval power in the Caribbean area, the four big ships were used as transports. They were returned to their owners in September 1898, but reentered Navy service as troop transports during the First World War.